Cerebellar damage causes motor coordination deficits or 'ataxia'-movements are variable and inaccurate, despite normal strength. Why cerebellar damage leads to these deficits is not understood. One prominent theory is that the cerebellum calibrates and maintains subconscious internal models, or knowledge of dynamic properties (e.g. inertia, viscosity), of body parts and objects. This project is aimed at testing this theory and determining whether a robotic device can be used to compensate for these deficits. The first aim will examine whether movement deficits are due to a misestimate of arm dynamic properties in the cerebellum, and whether it can be compensated for. This will be accomplished by comparing arm movements of individuals that have cerebellar damage with movements of control subjects and with simulations using computational models. An exoskeleton robot will then be used to correct for the identified movement impairments. The second aim will examine whether cerebellar deficits extend beyond movement control to perception of dynamic properties. It is expected that these individuals will not have basic sensory deficits (e.g. limb position sense), but will have difficulty perceiving dynamic properties that rely on both movement and sensory processing. Based on these findings, the robot will be used to test strategies for improving perceptual deficits. The investigator will receive training in neuroscience, neurology, mathematics, and robotics in order to conduct this work. This will be accomplished through didactic work, seminar attendance, and hands on training in the laboratory. This work is important for understanding and developing novel rehabilitation treatments for individuals with cerebellar damage. It is particularly important because there are currently no proven treatments for cerebellar ataxia.